Variable-Length Steering Shaft Sliding Coating Without Flow Seams

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Solution Overview

Problem

Existing methods for producing variable-length steering shafts with injection molding face challenges in achieving precise and defect-free sliding coatings, leading to issues like flow seams and dimensional inaccuracies due to collision of flow fronts during the injection process.

Innovation Solution

The method involves injecting molten plastic from one axial end of the mold cavity, using a gate point at an end wall to create a uniform flow front that fills the mold cavity in an axial direction, avoiding circumferential collisions and ensuring accurate positioning of the shaft core within the injection molding tool, which results in a uniformly thick and accurate plastics sliding coating.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If injection is performed via a single gate point in the axial direction within the toothing region, then the injection process is simplified, but flow seams and shaped defects occur due to flow front collision

Engineering Contradiction:

Improveinjection process simplicityVSAvoidsliding coating quality

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The injection process is divided into two independent stages: first injecting plastic into the gate chamber through a single gate point, then injecting into the mold cavity through multiple gate points arranged circumferentially. This segmentation prevents flow front collision while maintaining manufacturing simplicity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A gate chamber is introduced as an intermediary component between the injection system and the mold cavity. The gate chamber receives plastic through a single gate point and distributes it uniformly to multiple gate points, preventing direct flow front collision in the toothing region.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of manufacture

If radial injection is performed from the outside into the mold cavity, then the injection process is straightforward, but flow seams occur when flow fronts collide on the side opposite the gate point

Engineering Contradiction:

Improveinjection process simplicityVSAvoidflow seams and injection defects

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The single radial injection process is segmented into two phases: first filling the gate chamber, then distributing plastic through multiple circumferential gate points into the mold cavity. This eliminates flow front collision while maintaining process simplicity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The injection approach transitions from a single-point radial injection to a multi-point circumferential injection pattern. By distributing injection points around the circumference, the method prevents flow front collision that occurs with single-point injection.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Productivity

If the shaft core is positioned in the injection molding tool, then the sliding coating can be applied, but positioning accuracy is difficult to maintain without additional positioning elements

Engineering Contradiction:

Improvemass production efficiencyVSAvoidshaft core positioning accuracy

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The shaft core's own toothing structure is utilized as the positioning feature. The toothing on the shaft core engages with corresponding features in the mold, enabling self-positioning and self-centering without requiring additional positioning elements, thus maintaining both productivity and precision.

Inventive Principle:

Principle #25Self-service

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach minimizes injection defects, such as flow seams, and ensures high accuracy in the toothing region, improving the sliding characteristics and reducing manufacturing outlay, thereby enhancing the consistency and performance of the steering shaft.

Implementation Method 1

the injection of the molten plastic into the mold cavity between the shaft core and the mold surface of the mold cavity

Methodology Applied

Scientific EffectInjection molding:

Implementation Method 2

the flow front during the injection of the molten plastic propagates from the gate point in each case both axial and circumferential directions

Methodology Applied

Scientific EffectViscous flow:

Implementation Method 3

injecting molten plastic from one axial end of the mold cavity, using a gate point at an end wall to create a uniform flow front that fills the mold cavity in an axial direction

Methodology Applied

Scientific EffectCooling and solidification:

Data Source

PatentUS10919560B2Method for producing a variable-length steering shaft

Publication Date: 2021.02.16 THYSSENKRUPP PRESTA AG

AI summary

A method may be employed to produce a variable-length steering shaft. The method may involve positioning a shaft core within a mold cavity of an injection molding tool coaxially with respect to a mold surface that delimits a toothing region, injecting molten plastic into the mold cavity between the shaft core and the mold surface of the mold cavity, removing a toothed shaft from the injection molding tool after the molten plastic has solidified, providing a hollow shaft and axially inserting the toothing region into an internal toothing of the hollow shaft. To make it possible to provide an improved sliding coating with the least possible manufacturing outlay, the injection of the molten plastic may be performed from one axial end region of the mold cavity.